The present invention relates to an electronic part constituted by sealing a chip device in a cavity of a resin container and a manufacturing method therefor.
In recent years, size reduction and improvement in the performance of a variety of electronic apparatuses, such as portable telephones and personal computers, have proceeded. Therefore, size reduction, improvement in the reliability, cost reduction and so forth of the electronic part are required to be flexibly adaptable to dense mounting, such as chip-on-board mounting with which a multiplicity of bare chip devices (bare chips) are directly mounted on a printed circuit board.
In addition to the conventional resistors, capacitors, coils and semiconductor devices, the electronic parts for use in the electronic apparatus have been varied which include, for example, electro-optic devices and surface-acoustic-wave devices, which incorporate mechanically weak materials, such as the ferroelectric piezoelectric single-crystal substrates. In the foregoing circumstance in which the electronic parts have been varied, optimum mounting must be performed to protect the surface of the electronic part while considering adaptation to common use and standardization. Since the materials for use in the electronic parts have been varied recently, the conventional rough method of directly covering the surface of a passive device or a transistor, with a silicon resin or an epoxy resin cannot realize satisfactory reliability because resistance against thermal stress and mechanical impact is unsatisfactory.
Therefore, the electronic parts including the electro-optical devices or the surface-acoustic-wave devices which use mechanically weak materials, have been mounted by a method of, for example, forming a cavity in a resin container and mounting a chip in the cavity.
FIGS. 6A and 6B are perspective views showing the structure of a conventional electronic part which is a surface-acoustic-wave device taken as an example. Initially, a chip device 32 is mounted on a resin board 31. Then, an adhesive agent is applied to the peripheral portion of the upper surface of the resin board 31 or an adhesive sheet layer is interposed. Then, a frame 33 is overlaid around the chip device 32 such that accurate locating is performed. Then, while pressure is being applied, a first heating and bonding process is performed to bond the frame 33 to the resin board 31 (see FIG. 6A). Then, while close attention is being paid to prevent discharge of the adhesive agent from the top end of the frame 33 and omission from the application of the adhesive agent, an adhesive agent or the like is applied to the upper surface of the frame 33, the cover 34 is mounted on the frame 33, and then a second heating and bonding process is performed such that pressure is again applied (see FIG. 6B). As described above, the bonding process is performed such that the application of the pressure and heat are performed two times. Then, a resin container 30 having a cavity 35 in which the chip device 32 is accommodated is formed. Thus, the electronic part has been manufactured.
The reason why the flat resin boards are superimposed to form a multilayer structure similar to a sandwich is that the manufacturing cost must be reduced. Examples of the foregoing structure have been disclosed also in Japanese Patent Laid-Open No. 2-179018. With the conventional technique, the chip device 32 is mounted on the resinboard 31, and then the frame 33 is bonded. Another example is structured such that the frame 33 is bonded to the upper surface of the resin board 31 to form a recess on which the chip device 32 is mounted.
However, the above-mentioned conventional technique is required to accurately locate the bonding positions whenever the resin board is overlaid. When the size of the electronic part is furthermore reduced, the relative positions among the boards and the positions of the adhesive agents and the adhesive layers must accurately be located whenever the board is overlaid. Thus, there arises a problem in that satisfactory productivity cannot be realized and the operation cost cannot be reduced.
In general, plastic deformation of the resin board easily occurs when the resin board is heated or pressed. When the adhesive process for heating the resin board while applying pressure to the resin board is performed repeatedly, the amounts of deformation is accumulated excessively to perform accurate locating. What is worse, the sealing characteristic deteriorates, leak easily takes place and the reliability deteriorates. When the process for bonding the resin boards to each other is performed by using a prepreg or an adhesive resin, the bonded prepreg or the adhesive resin is softened or deformed if the pressure and heat are applied afterwards. Therefore, there arises a problem in that the resin components seep and the resin container is deformed and distorted. Another problem arises in that a portion of the resin component is gasified and the inside portion of the resin container is filled with the gas. In this case, the gasified resin adheres to the surface of the chip device. Thus, the chip device is contaminated.